Electrode leads of the generic type are well known from the prior art. They serve as an electrical connection between an electrotherapeutic implantable device, which may be a neurostimulator, pacemaker, defibrillator or other suitable electrotherapeutic implantable device, and the location being treated in the body. These may be whole variety of locations in the body. One example given here is a cardiac electrode lead. The electrode leads not only serve to transmit therapeutic pulses, but they also serve to transmit body and measurement signals to the implant, so that an appropriate treatment can take place specifically in response to the body signals. This treatment may represent a stimulation pulse that is suitable for replacing the missing stimulus generation. The treatment may also be a high-energy defibrillation pulse.
In medical technology the term electrode lead is referred to in short, as “electrode”. It refers in this definition not only to the point of transition of the electric energy according to the physical definition, but it also refers to the line consisting of the electrical conductor including its enveloping insulation, as well as to all other functional elements that are permanently connected to the line. For reasons of clarity, the section of the electrode that actually functions within the physical meaning, which includes the point of transition of the electric energy, will be referred to below as “electrically active region”.
Measures must be taken to ensure that a long-term implantation in the body—i.e., in a highly corrosive environment—occurs without significant degradation processes and does not result in an undesirable immunological reaction.
For the region of the long stretched-out feed line, which must, of course, be electrically insulated toward the outside, biocompatible synthetic materials present themselves. The most important synthetic material in this context is silicone rubber.
For the region of the electrically active region it is important to take into consideration electrophysical effects. An electrically active region of an implantable electrode must have a low electrical resistance. This is decisive for a successful emittance of stimulation pulses, since an implantable medical device is dependent upon an independent power supply. This power supply is ensured by means of a battery, which, obviously, has a limited size.
To be avoided is the formation of a corrosion layer, which causes the electrical resistance to increase, with the consequence that endogenous signals can not be transmitted correctly to the implantable medical device. Also, the energy output increases as well.
Regarded as commonly used material with high bioresistance, but also with high electrical resistance, are cobalt-chrome alloys (e.g. MP35N). Platinum, iridium, or an alloy of these two metals are also regarded as bioresistant materials. The platinum-iridium alloys, in particular, are known for having a high electrical resistance.